1. Field of the Invention
The invention relates to an apparatus and method for inputting information, and more particularly, to a 3D input apparatus and method thereof for restoring a spatial position of the apparatus.
2. Description of the Related Art
Conventionally, an input apparatus including a 2-dimensional sensor array, such as an LCD tablet or a digitizer table, has been widely used to input handwritten data using a pen into a personal portable terminal or a computer appliance. Such an input apparatus requires an additional sensing plane surface where a large 2-dimensional sensor array is disposed. Thus, the input apparatus not only occupies a predetermined space, but is also inconvenient for carrying, and very expensive.
Recently, there has been an increased demand for small-sized personal portable terminals, and watch-type or purse-type portable terminals have been developed. Due to this growing tendency to scale down portable terminals, display screens have also been scaled down. Thus, inputting data by natural handwriting using a conventional tablet is difficult.
Accordingly, it may be effective to enable document input using only a single electronic pen on an ordinary plane surface, instead of on a physical tablet. That is because the single electronic pen can provide a larger input space than a conventional pen input device does, and subsequently enable natural handwriting input.
Such an electronic pen, enabling the input on the ordinary plane surface, operates in a self-movement sensing manner. To input a document or a picture using the electronic pen, positions of the pen's tip in a reference coordinate system should be obtained successively. However, in most cases, while the electronic pen is in contact with the plane surface in a state of handwriting, it is separated from the plane surface in a state of non-handwriting or moving. Accordingly, a device is required for precisely measuring positions of the pen even while the pen is separated from the plane surface.
To overcome these problems, U.S. Pat. No. 5,902,968 and U.S. Pat. No. 5,981,884 disclose a method of obtaining positions of a tip of a pen that includes a 3-axis acceleration sensor and a 3-axis Gyro sensor. In this method, a typical inertial navigation system (INS) is applied in the electronic pen. The 3-axis acceleration sensor, mounted on the electronic pen, measures accelerations on the x-, y-, and z-axes, and the 3-axis Gyro sensor measures Euler angles that are expressed as a roll angle Φ, a pitch angle Θ, and a yaw angle Ψ. Thus, a posture and an acceleration of the pen in an absolute coordinate system are measured such that a user's handwriting is reproduced.
A position of the above-described electronic pen is detected by doubly integrating the acceleration that is obtained using the acceleration sensor. Since an error obtained from the acceleration sensor is also doubly integrated, however, the positional error caused by the acceleration error greatly increases over time so that the position of the electronic pen cannot be accurately detected.